The present invention relates to a secure method of using video to detect persons or objects, and also to a system enabling the method to be implemented.
The invention applies particularly, but not exclusively, to automatic or semiautomatic control of systems for transporting people, such as moving staircases (escalators) or travelators.
Naturally, the invention can also be applied to conveying goods, to detecting objects or persons in approach zones of or close to transport systems, or indeed in the vicinity of doors giving access to zones that are to be kept secure.
At present, whenever it is desired to start or restart a moving staircase or a travelator following a stoppage, whether normal or in an emergency, it is necessary for safety reasons for a person to verify that no person or object is to be found on the staircase or travelator.
In addition, automatic starting following detection of a person approaching the transport system must not be performed until it has been ensured that there is no passenger or object in a predefined safety zone.
Finally, during normal stoppages of the transport system, it is necessary to verify that there is nobody on the system before stopping it.
In French patent application No. 2 773 791, proposals have already been made for a control system including video cameras that provide images of stationary and/or moving portions of the mechanical device that is to be controlled. That system continuously compares the images received from the cameras with reference images taken in the absence of persons on the controlled mechanical device in order to determine whether people are on the mechanical device or in an approach zone thereto, and in order to cause the device to be stopped or started as a function of the presence or absence of people in the received images.
It is found that that system does not provide sufficient safety in operation, and as a result it has not been approved by the official approval bodies concerned. In particular, such a system is not designed to warn of faults in its own operation and it does not make it possible to guarantee that information it provides concerning the presence or the absence of a person or an object on the mechanical system is reliable information.
An object of the present invention is to eliminate that drawback. This object is achieved by providing a method for detecting persons or objects in a detection zone in order to control a mechanical system such as a transport device as a function of presence of objects or persons detected in the detection zone by means of cameras displayed in such a manner as to cover the detection zone and connected to a monitoring processor coupled to a control device for controlling the mechanical system.
According to the invention, the method comprises:
an initialization phase comprising a step of checking hardware elements of the monitoring processor and data stored in the monitoring processor;
a processing loop including, for each active camera, a step of acquiring an image supplied by the camera and of processing the image in order to generate detection data whenever a person or an object is detected in the detection zone and in order to determine which commands to apply to the control device of the mechanical system, a step of checking the quality of the image, a step of checking the position of the camera relative to the detection zone, and a step of checking hardware elements of the monitoring processor and data stored in the monitoring processor; and
a phase of checking and controlling the control device using commands determined in the processing loop and as a function of any defects detected during the checking step.
By means of the set of checks and tests that it performs, the monitoring processor provides the control device of the system to be controlled with information concerning the presence of persons or objects, in which said presence is detected with a very high level of reliability. This ensures that the commands applied to the control device of the system to be controlled are consistent and appropriate.
Advantageously, the checks performed during the processing loop are periodic, each check having an execution period adapted as a function of the critical nature and the probability of failure of the element or the data being checked.
According to a feature of the invention, the step of checking image quality consists in determining the mean luminance of analyzed zones of the image and in comparing the mean luminance with high and low thresholds, image quality being considered as satisfactory if the mean luminance lies between the high and low thresholds.
According to another feature of the invention, the step of checking the position of each camera consists in analyzing specific predefined zones in the images supplied by the camera in order to determine whether said zones present predetermined characteristics, and if these zones do not present said predetermined characteristics, then the camera is considered as being faulty because it has been moved.
Preferably, the method further comprises a step of updating reference images in order to adapt to variations in ambient luminosity in the detection zone.
Also preferably, the method further comprises a step of checking the image processing algorithm, which step consists in running the image processing algorithms on a video test pattern, and in comparing the results obtained with reference values.
Advantageously, data checking relates to parameter data, reference image data, and programs executed by the monitoring processor.
The invention also provides a secure system for detecting persons or objects in a detection zone in order to control a mechanical system such as a transport device, the detection system comprising a set of cameras covering the detection zone and a monitoring processor coupled to the cameras and to a control device for controlling the mechanical system.
According to the invention, the system comprising:
means responsive to each active camera in succession to acquire and process an image supplied by the camera, and to determine the commands that are to be applied to the control device;
means for checking the image quality and the position of each camera relative to the detection zone during image acquisition and processing;
means for checking the hardware elements of the processor and the data stored in the processor, during image acquisition and processing and during a stage of initializing the processor; and
means for checking and controlling the control device for controlling the mechanical system by means of commands that are generated providing no error is detected by the check means.
According to a feature of the invention, the system further comprises means for determining the ambient luminosity of the detection zone, and for updating reference image data as a function of variation in ambient luminosity.
According to another feature of the invention, the system further comprises means for determining the mean luminance of analyzed zones of the image and for comparing the mean luminance with high and low thresholds, the quality of the image being considered as sufficient if the mean luminance lies between the high and low thresholds.
According to another feature of the invention, the system comprises means for cyclically checking proper operation of memories of the processor.